Effects

import React from 'react'
import ReactDOM from 'react-dom'
import {createEffect, createStore} from 'effector'
import {useStore,useEvent} from 'effector-react'

const fetchUserFx = createEffect(url => fetch(url).then(req => req.json()))

const $user = createStore(null).on(
  fetchUserFx.doneData, (state, result) => result.username,
)

const url =
  'https://gist.githubusercontent.com/' +
  'zerobias/24bc72aa8394157549e0b566ac5059a4/raw/' +
  'b55eb74b06afd709e2d1d19f9703272b4d753386/data.json'

const App = () => {
  const user = useStore($user)
  const pending = useStore(fetchUserFx.pending)
  const fetchEvent = useEvent(fetchUserFx)
  return (
    <div>
      {user ? <div>current user: {user}</div> : <div>no current user</div>}
      <button disable={pending} onClick={() => fetchEvent(url)}>
        load user
      </button>
    </div>
  )
}

ReactDOM.render(<App />, document.getElementById('root'))

Try it